98 



LACRYMAL ORGANS. 



as several scinci, which may be drawn over the 

 eye without interrupting vision, the cornea cor- 

 responding to it." This is the structure in the 

 frog ; for what Cuvier admitted as a third eye- 

 lid is horizontal instead of vertical, and, as 

 Carus has shown, nothing more than the lower 

 eyelid. In the frog the upper eyelid follows 

 the motions of the eyeball. The lower eyelid 

 has independent motion ; admitting of being 

 drawn over the eye and falling into a fold when 

 this is open. 



The anterior and posterior semilunar folds in 

 certain fishes have been already alluded to. 



The glandule of Harder. The glandule of 

 Harder belongs peculiarly to the membrana 

 nictitans or third eyelid ; it therefore does not 

 exist in man and the quadrumana. The lacry- 

 mal caruncle is not the representative of it, as is 

 asserted in Dr. Grant's Treatise on Compara- 

 tive Anatomy, for both may exist together. I do 

 not even know if it is correct to say that the 

 two structures are developed in an inverse 

 ratio, for in the sheep, in which the glandule of 

 Harder is of considerable size, the caruncula is 

 absolutely as great, if not greater, than that of 

 man. Even among the hare kind, which have 

 the membrana nictitans and glandule of 

 Harder much developed, I find, particularly 

 in the rabbit, a trace of lacrymal caruncle as 

 scattered follicular grains along with small 

 hairs at the inner canthus. It is only in birds 

 that we lose all trace of the lacrymal caruncle. 



The glandule of Harder is situated in the 

 orbit between its inner wall and the globe of 

 the eye. In the sheep, for instance, the glan- 

 dular substance is collected around the cartila- 

 ginous pedicle of the membrana nictitans, 

 on the inner surface of which it opens by two 

 or three small ducts. In the elephant, in which 

 the lacrymal gland is said to be wanting, or 

 very small, the glandule of Harder is said to 

 be very large. It opens between the membrana 

 nictitans and the eyeball by an opening the 

 size of a quill. In the hare kind, as has been 

 said, the glandule of Harder is immense. It 

 presents two lobes, and its duct opens in a 

 wide lacuna within the membrana nictitans. 

 According to Miiller,* the elementary particles 

 or ends of the ducts are minute vesicles every- 

 where equal and joining in the manner of 

 branches into irregular oblong lobes. The 

 excretory duct at the external surface of the 

 gland opposite the eye is divided in the bi- 

 lobated glandular mass into a great number of 

 smaller ducts, which divaricating are joined 

 each to a branch of the lobules. 



In birds the glandule of Harder is commonly 

 much more considerable than the lacrymal 

 gland. It lies as usual at the nasal canthus 

 and opens within the third eyelid towards the 

 eyeball. There is never any caruncle. Miiller 

 tells us the glandule of Harder in birds is 

 easily injected with mercury after its secretion 

 has been all pressed out. The surface of the 

 organ is divided into many smaller lobes. The 

 internal ramification of the ducts does not ap- 

 pear to be complicated. 



* De glandularum secernentium penit ; ori struc- 

 tura, p. 5), tab. v. fig. 6 and 7. 



In reptiles the glandule of Harder is smaller 

 than the lacrymal gland. 



The secretion of the glandule of Harder is a 

 thick transparent viscid matter. 



111. Secreting and derivative lacrymal 

 apparatus. The development of the lacrymal 

 gland and of that of Harder is generally in an 

 inverse ratio. It would appear that the deriva- 

 tive lacrymal apparatus is more in relation with 

 the lacrymal gland than with the glandule of 

 Harder, as it is much developed in man, in 

 whom there is no glandule of Harder, and, as is 

 reported, it is wanting in the elephant, in which 

 the glandule of Harder is said to be very 

 large. The lacrymal gland exists in man, apes, 

 sapajous, and snakes, but no glandule of 

 Harder. In all other mammifera there is both 

 a lacrymal gland and a glandule of Harder. In 

 proportion as the latter enlarges the former be- 

 comes smaller. Among the cetacea, the dol- 

 phin possesses a lacrymal gland which sur- 

 rounds the eyeball like a ring. Its excretory 

 ducts, which are numerous, open on the inner 

 surface of both upper and lower eyelids. The 

 derivative lacrymal apparatus is wanting; in 

 this respect, seals and walrusses agree with the 

 cetacea.* Other mammals, as moles and shrew- 

 mice, are said to present no trace of lacrymal 

 apparatus. In the elephant, small glandular 

 grains the size of a pea are said to represent the 

 lacrymal gland. Camper says the hippopo- 

 tamus has no puncta, from which may be in- 

 ferred the absence of any lacrymal passage into 

 the nose. The elephant is also said to want 

 the derivative lacrymal apparatus. 



In birds the lacrymal gland is small, and lies 

 at the posterior angle of the eye, either towards 

 the roof or the floor of the orbit. The derivative 

 lacrymal organs in the common fowl, for in- 

 stance, consist of two large lacrymal points, the 

 upper the larger, and a membraneous canal 

 leading into the nose. 



In reptiles, the lacrymal gland lies behind the 

 eyeball, and is of considerable size, especially 

 in harmless serpents. According to Duverney, 

 the lacrymal gland in one species of typhlops 

 is six times larger than the extremely diminu- 

 tive eyeball; but even in poisonous serpents, 

 the viper for instance, it is large. 



The sauria and chelonia have for the most 

 part both a lacrymal gland and a glandule of 

 Harder, the former the larger. Batrachia want 

 the lacrymal apparatus. 



In serpents the secretion of the lacrymal 

 gland is poured into the oculo-palpebral space, 

 from which a lacrymal duct leads. In the 

 colubri there is, in the fore and lower part of 

 the oculo-palpebral space, a hole or round 

 pore, in some individuals seen with difficulty, 

 very distinct on the contrary in others, and 

 which may admit a bristle. This is the lacry- 

 mal point; it is single and is continuous with 

 a very slender membranous duct, semi- 

 transparent, which forms the lacrymal canal. 

 This, in harmless serpents, opens into a large 

 pouch communicating with the mouth in front 



* Rapp. 1. c. Rapp describes, in the Cetacea, 

 scattered grains of lacrymal gland, which open on 

 the conjunctiva near the eyeball. 



